In order for a print imaging support to be widely accepted by the consumer for imaging applications, it has to meet requirements for preferred basis weight, caliper, stiffness, smoothness, gloss, whiteness, and opacity. Supports with properties outside the typical range for ‘imaging media’ suffer low consumer acceptance. In addition to these fundamental requirements, imaging supports are also subject to other specific requirements depending upon the mode of image formation on the support. These requirements include penetration by liquid processing chemicals, ready wettability by ink, quick drying and the ability to maximize transfer of dye from the donor, which results in a higher color saturation. Other properties, such as recyclability and resistance to curl, are desired for imaging supports.
It is important for an imaging media to simultaneously satisfy several requirements. One commonly used techniques in the art for simultaneously satisfying multiple requirements includes the use of composite structures comprising multiple layers. However, multiple operations are required to manufacture and assemble all of the individual layers. There is a need for imaging supports that can be manufactured in a single in-line manufacturing process while still meeting the stringent features and quality requirements of imaging supports.
The stringent and varied requirements of imaging media demand a constant evolution of material and processing technology. One such technology, known in the art as ‘polymer foams’, has previously found significant application in food and drink containers, packaging, furniture, and appliances. Polymer foams have also been referred to as cellular polymers, foamed plastic, or expanded plastic. Polymer foams are multiple phase systems comprising a solid polymer matrix that is continuous and a gas phase. For example, U.S. Pat. No. 4,832,775 discloses a composite foam/film structure which comprises a polystyrene foam substrate, oriented polypropylene film applied to at least one major surface of the polystyrene foam substrate, and an acrylic adhesive component securing the polypropylene film to the major surface of the polystyrene foam substrate. The foregoing composite foam/film structure can be shaped by conventional processes, such as thermoforming, to provide numerous types of useful articles including cups, bowls, and plates, as well as cartons and containers, that exhibit excellent levels of puncture, flex-crack, crease and abrasion resistance, moisture barrier properties, and resiliency.
Foams have also found application in imaging media. For example, JP 2839905 B2 discloses a 3-layer structure comprising a foamed polyolefin layer on the image-receiving side, raw paper base, and a polyethylene resin coat on the backside. The disclosure of JP 09127648 A highlights a variation of the JP 2839905 B2 structure, in which the resin on the backside of the paper base is foamed, while the image receiving side resin layer is unfoamed. Another variation is a 4-layer structure, highlighted in JP 09106038 A, in which the image receiving resin layer comprises 2 layers, an unfoamed resin layer which is in contact with the emulsion, and a foamed resin layer which is adhered to the paper base. Means of making foam core imaging elements, including glossy-surfaced elements, are disclosed in U.S. Pat. Nos. 6,537,656, 6,447,976, 6,566,033 and 6,514,659 and U.S. Application Publications 2003/0219663, 2003/0219610, 2003/0152760, 2003/0128313, 2003/0118750, 2003/0123150, 2003/0118807 and 2003/0118750. These imaging elements possess the typical surface roughness of conventional imaging elements, that is, these elements have a surface feature range of between 0.1 and 1.1 microns.
In the case of resin coated photographic prints, the layer immediately below the emulsion has a large impact on the image sharpness of the print due to the scattering of light during exposure of the print paper to the negative, as disclosed in To RC or Not to RC, Crawford, Gray and Parsons, Journal of Applied Photographic Engineering, 110–117 (1979). Large amounts of TiO2, in the 10 to 15 percent range or higher, are added to this layer to enhance image sharpness and, in turn, hiding power and opacity of the imaging support. Given the fact that ink jet, thermal, and most high end imaging media were derived from and are now in competition with photographic imaging media, the need for comparable degrees of opacity become necessary.
Foamed materials utilized as reflective support suffer from surface pits, especially when the foamed material is plastic coated on the side that will be used for the imaging layer. Pits are defects that first appear at the surface of a polycoated layer after lamination on relatively smooth or “glossy” chill rolls. During high-speed coating, trapped air between the chill roll and the plastic coating leaves a surface hole, creating a smooth and rounded defect. Later emulsion-coating operations replicate the hole into the emulsion layer. Specular illumination of the imaged side causes these emulsion defects to reflect points of brilliance, a distraction when viewing dark areas on the print.
Unfortunately, the typical foam composite imaging material that meets the requirements of an imaging support has naturally more surface roughness at the spatial frequencies that correspond with the size of pits. The control of the surface roughness of the foam core is difficult, as foamed polymer sheet surfaces are prone to pits, resulting in pits in the image unless high levels of polymer layers are coated on top to smooth the surface. There remains a need for improved foam core imaging elements than those disclosed in the prior art.